JP2000131514A - Variable optical path delaying device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive and small-sized variable optical path delaying device. SOLUTION: This delaying device is constituted of a rotary disk part 3 rotating around a central axis, a spiral slope reflection mirror 1 formed on the rotary disk part 3 and a vertical reflection flat mirror 2 reversing an advance direction of a beam reflected by the spiral slope reflection mirror 1. It has a structure scanning a length of an optical path that an incident beam passes till it is returned again, and it is combined with an interferometer to be used for a Fourier transform spectroscopic interferometer and an autocollimator, etc. The optical path length scan speed is fixed to a high speed, and its inexpensiveness and miniaturization are made possible while keeping high resolution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable optical path delay device which is small and can scan a long optical path length at a stable scanning speed, and relates to an interferometer for Fourier transform spectroscopy and an interferometer constituting an autocorrelator. It is used as a part.

[0002]

2. Description of the Related Art Conventionally, as a variable optical path delay device for generating an optical path length difference using a rotary motion, a device for rotating a corner cube mirror has been known (Japanese Patent Application No. 4-2 / 1990).
No. 51915). FIG. 9 is a configuration diagram of a conventional interferometer. In this interferometer, parallel light from a light source is divided into two, reflected light and transmitted light, by a beam splitter BS, reflected by deflecting mirrors M1a, M1b, respectively, and passed through optical paths LPa, LPb to the same corner cube mirror CM. Incident.

An optical path LPa is connected to a corner cube mirror CM.
The light that is incident and reflected through the mirror is then incident on the plane mirror M2a and vertically reflected, and the light that is incident on the corner cube mirror CM via the optical path LPa and then reflected is incident on the plane mirror M2b and vertically reflected. Again travel in the opposite direction via the corner cube mirror CM, are multiplexed again by the beam splitter BS, and interfere with each other. The optical path length scanning is performed by eccentric rotation about the rotation axis AX.

[0004]

The corner cube mirror used in the interferometer having such a structure is large and expensive. In addition, it is necessary to set an eccentric rotation axis on the corner cube mirror, which requires time and effort for production. Furthermore, high-speed rotation was difficult due to eccentric rotation.

The present invention has been made in view of the above circumstances, and uses a rotating spiral slope structure or a spiral staircase structure as a reflecting mirror or a delay plate, and utilizes the fact that the optical path length changes with the rotation of a disk to achieve high speed and high speed. An object of the present invention is to compactly configure an optical path delay device that stably performs long-distance optical path length scanning.

[0006]

According to the present invention, there is provided an optical delay device for controlling the length of an optical path by changing the position of a reflecting mirror. Part and a mirror formed in a spiral slope shape around the disk, light is incident on the spiral slope mirror, and the incident position on the mirror surface is translated with respect to the incident optical axis by rotation. The distance until the incident light reaches the mirror surface is changed to control the optical path length through which the incident light passes by the rotation of the disk. The slope structure is characterized in that the incident light is reflected by using one surface.
Further, the slope structure is characterized in that incident light is reflected using both surfaces.

According to another aspect of the present invention, there is provided an optical delay device for controlling an optical path length by changing a position of a reflecting mirror, comprising: a disk portion rotatable with respect to a central axis; It is composed of a mirror formed in a spiral staircase shape in the surrounding part, and the light is incident on the spiral staircase mirror, and the incident position on the mirror surface is moved in parallel to the incident optical axis by rotation, so that the incident light is mirrored. The optical path length through which the incident light passes by rotating the disk is controlled by changing the distance until the light reaches the optical disk. The staircase structure is characterized in that the incident light is reflected using one surface. Further, the staircase structure is characterized in that incident light is reflected using both surfaces.

According to another aspect of the present invention, there is provided an optical delay device for controlling an optical path length by changing a thickness of a delay plate through which light is transmitted, the optical delay device being rotatable about a central axis. A disk portion, which is constituted by a delay plate formed in a spiral slope type around the disk, and light is incident on the spiral slope delay plate;
By controlling the optical path length through which the incident light passes by rotating the disk by changing the distance that the incident light transmits through the delay plate by rotating the exit position on the spiral slope parallel to the incident optical axis by the rotation. It is characterized by.

According to another aspect of the present invention, there is provided an optical delay device for controlling an optical path length by changing a thickness of a delay plate through which light passes, wherein the optical delay device is rotatable with respect to a central axis. A disk portion and a delay plate formed in a spiral step shape on the disk portion. Light is incident on the spiral step delay plate, and the incident position on the spiral step is parallel to the incident optical axis by rotation. By moving the optical disk, the distance that the incident light transmits through the delay plate is changed, and the optical path length through which the incident light passes by the rotation of the disk is controlled.

In the present invention, since the spiral slope structure or the spiral staircase structure is used, the direction in which the incident light is reflected or refracted is constant even if it is rotated. Light reflected or refracted from the spiral staircase structure can be returned to the incident direction. At this time, the optical path length through which the light beam passes depends on the rotation angle of the rotating disk, and changes with the rotation. In the present invention, an optical path length scanning mechanism is configured using this function.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a reflecting mirror or a delay plate having a spiral slope structure or a spiral staircase structure is used and is installed symmetrically with respect to a rotation axis. As a result, since a corner cube is not used, the size and the cost are reduced. Further, high-speed and smooth rotation can be achieved as compared with a conventional variable optical path delay device for eccentrically rotating a corner cube. It differs from the prior art in that it is rotated using a helical structure. Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following embodiments are examples in which the present invention is used for an interferometer for Fourier transform spectroscopy.

(Embodiment 1) FIG. 1 is a configuration diagram showing an embodiment of an optical path length scanning mechanism using a spiral inclined reflecting mirror according to the present invention.

In FIG. 1, 1 is a helical inclined surface reflecting mirror, 2 is a vertical reflecting plane mirror, 3 is a rotating disk, 4 is a rotating axis, 5 is a light source, 6 is a collimator lens, 7 is a light splitting mirror, and 8 is fixed reflection. A mirror, 9 is a condenser lens, and 10 is a photodetector.

In order to operate this, the light from the light source 5 is collimated by the collimator lens 6 and is incident on the light splitting mirror 7. The incident light is split by the light splitting mirror 7, one of which is reflected toward the fixed reflecting mirror 8, returns to the light splitting mirror 7, and the other is reflected by the spiral inclined reflecting mirror and the vertical reflecting flat mirror, and then the reverse path is used. And returns to the light splitting mirror 7. These light beams are recombined by the light splitting mirror 7 and condensed on the photodetector 10 by the condenser lens 9 to obtain an interference signal.

Here, when the rotating disk 3 is rotated around the rotating shaft 4, the rotating disk 3 rotates around the rotating shaft 4 of the spiral inclined reflecting mirror 1 installed on the rotating disk 3. At this time, the optical path length of the optical path passing through the vertical reflecting plane mirror can be changed periodically. When the signal of the photodetector 10 is measured in synchronization with the rotation of the rotating disk, an interferogram is obtained. The spectrum of the incident light is obtained by Fourier-transforming the interferogram.

FIG. 2 is an explanatory diagram of a change in the optical path length. As shown in FIG. 2, the optical path changes as the spiral inclined mirror rotates. A path OAB indicates an optical path when light is incident on the uppermost portion (point A) of the spiral inclined reflecting mirror,
The light incident from the point O in parallel with the rotation axis is a spiral slope reflecting mirror 1
The light is reflected at a point A on a and returns to the incident direction by reciprocating a distance to a point B on the plane of incidence mirror 2. The path OCD shows an optical path when the rotating disk is rotated by θ and light is incident on the point C on the helical inclined reflecting mirror 1b. Return to the direction. Further, the ray path after the disk portion makes one rotation is shown as a path OEF. It reciprocates to a point F on the vertical incidence plane mirror 2 via a point E on the spiral inclined reflecting mirror 1c and returns to the incident direction.

Here, the intersection of the line EF with the line drawn vertically from A to the line EF and the line EF are defined as G, and the intersection of the line AG and the line CD is defined as H. At this time, it is obvious that the lengths of the straight line AB, the straight line HD, and the straight line GF are equal. Assuming that the optical path length is 2AB when the light ray is innermost at the top of the spiral inclined reflecting mirror, that is, when the rotation angle of the rotating disk is zero,
The increment of the optical path length when the disk rotates by the angle θ is 2
AC + 2CH, and the increment of the optical path length when the disk portion makes one round is 2AE + 2EG.

Here, assuming that the radius of the rotating disk portion is R and the pitch of the spiral is d, the inclination angle α of the spiral slope with respect to the rotation axis is α = π / 2-tan ⁻¹ (2πR / d) (1) It is represented by If the light enters from point O, this light is reflected in the direction of angle 2α. The distance between AC is d
(Θ / 2π), the distance ΔL between the channels is ΔL (θ) = 2d (θ / 2π) ｛1 + cos (2α)｝ (2) Here, when the spiral slope makes one rotation, the optical path length difference becomes the maximum, and when this is ΔL _MAX , the following equation holds: ΔL (2π) = ΔL _MAX = 2d {1 + cos (2α)} (3)

Specific parameters in this embodiment are R = 25 mm, d = 8.5 mm, α = 54 mrad, and a value of ΔL _MAX of 3.4 cm is obtained from equation (3).
In the Fourier transform spectroscopy, the wave number resolution is 0.30 c since the wave number resolution is the reciprocal of the maximum optical path length difference ΔL _MAX.
m- ¹ . According to the present invention, it is possible to scan a long optical path length even if it is small, and thus such high wavenumber resolution is obtained.

(Embodiment 2) Next, an embodiment in which a longer optical path length can be scanned by the improvement of Embodiment 1 will be described. Example 1
In the above, only one surface of the spiral slope reflector is used, but in this embodiment, both sides of the spiral slope reflector are used. A schematic diagram is shown in FIG. In FIG. 3, reference numerals 2a and 2b denote vertical incidence plane reflecting mirrors, 3 denotes a rotating disk, 4 denotes a rotating shaft, 5 denotes a light source, 6 denotes a collimator lens, 7 denotes a light splitting mirror, 9 denotes a condenser lens, and 10 denotes a photodetector. , 11a and 11b are deflection mirrors, and 12 is a double-side polished spiral inclined reflecting mirror.

In the first embodiment, only one of the optical paths split by the light splitting mirror enters the spiral inclined reflecting mirror and the other enters the fixed reflecting mirror. In this embodiment, both optical paths are connected to both sides. The incident light is incident on the polished spiral inclined reflecting mirror 13.

By passing through the deflecting mirrors 11a and 11b, one optical path is incident on the upper surface of the spiral inclined mirror and the other optical path is incident on the lower surface of the spiral inclined mirror. The vertical incidence plane mirrors 2a and 2b are installed. Thus, when the optical path length on the upper side becomes maximum, the optical path length on the lower side becomes minimum, and vice versa. Therefore, it is obvious that the optical path length difference between the two optical paths is twice that in the first embodiment.

When a double-sided polished spiral inclined mirror having the same size as that of the first embodiment and a disk are used, the maximum optical path length difference is 6.8 cm.
Becomes In this case, the wave number resolution in Fourier transform spectroscopy is 0.15 cm ⁻¹ , and higher resolution can be achieved.

(Embodiment 3) FIG. 4 is a structural view showing an embodiment of an optical path length scanning mechanism using a spiral staircase reflecting mirror according to the present invention. In FIG. 4, 13 is a spiral staircase reflecting mirror, 3 is a rotating disk portion, 4 is a rotating axis, 5 is a light source, 6 is a collimator lens, 7 is a light splitting mirror, 8 is a fixed reflecting mirror, 9 is a condenser lens,
Reference numeral 10 denotes a photodetector.

In order to operate this, one of the light split by the light splitting mirror 7 is incident on the fixed reflecting mirror 8 and the other is incident on the spiral stair reflecting mirror. The light reflected by the step surface again enters the light splitting mirror 7, where it is multiplexed with the light returned from the fixed reflecting mirror 8 again, and is condensed on the photodetector 10 by the condensing lens 9, and the interference signal Get.

Here, the rotating disk unit 3 is driven to rotate the spiral staircase reflecting mirror around the rotation axis 4. At this time, the length of the optical path passing through the spiral staircase reflecting mirror can be changed periodically. When the signal of the photodetector 10 is measured in synchronization with the rotation of the rotating disk, an interferogram is obtained, and a spectrum is obtained by performing the Fourier transform.

The principle will be described below. The spiral staircase is a part of a fan shape obtained by equally dividing the circumference of the radius R into N, and the step difference is assumed to be Δd. When you go around the rotating disk,
The change in the optical path length of the light beam applied to the step surface of the spiral staircase is 2NΔd. Here are the specific parameters:
R = 25 mm, N = 2048, Δd = 0.633 μm, the maximum optical path length difference is ΔL _MAX = 0.26 cm, and the wave number resolution in Fourier transform spectroscopy is 3.8 cm ⁻¹ .

(Embodiment 4) Next, an embodiment in which a higher wavenumber resolution can be obtained by improving the embodiment 3 will be described. In the third embodiment, only one surface of the spiral staircase reflecting mirror is used. In the present embodiment, the spiral staircase reflecting mirror is formed on both sides of the rotating disk, and both surfaces are used. A schematic diagram is shown in FIG. In FIG. 5, 3 is a rotating disk, 4 is a rotating axis, 5 is a light source, 6 is a collimator lens, 7 is a light splitting mirror, 9 is a condenser lens, 1
0 is a photodetector, 11a and 11b are deflection mirrors, and 14 is a double-sided spiral staircase reflection mirror.

In the third embodiment, only one of the optical paths split by the light splitting mirror is incident on the spiral staircase reflecting mirror, and the other is incident on the fixed reflecting mirror. The light enters the front and back surfaces of the double-sided spiral staircase reflecting mirror 14. By passing through the deflecting mirrors 11a and 11b, one optical path is made incident on the upper surface of the spiral staircase reflecting mirror and the other optical path is made incident on the lower surface of the spiral staircase reflecting mirror to be reflected again. Return to the direction.

Thus, when the optical path length passing through 11a is maximum, the optical path length passing through 11b is minimum, and vice versa. Therefore, it is obvious that the optical path length difference between the two optical paths is twice that in the third embodiment. When a spiral staircase reflector and a disk having the same size as those of the third embodiment are used, the maximum optical path length difference is 0.52 cm and the wave number resolution is 1.9 cm ^-1 , so that higher resolution can be achieved.

(Embodiment 5) FIG. 6 is a block diagram showing an embodiment of an optical path length scanning mechanism using a spiral slope delay plate according to an embodiment of the present invention. In FIG. 6, 2c is a vertical reflecting plane mirror, 3 is a rotating disk, 4 is a rotating axis, 5 is a light source, 6 is a collimator lens, 7 is a light splitting mirror, 8 is a fixed reflecting mirror, 9 is a condenser lens, and 10 is light. The detector 15 is a spiral slope delay plate.

In order to operate this, light is vertically incident on the flat portion of the spiral slope delay plate. This light ray is transmitted through the retardation plate and then refracted and emitted in a certain direction. At this time, since the refracting surface is a helical slope, it is always constant in the emitting direction, and can be returned to the original direction by using a plane reflecting mirror perpendicular to the emitting direction.

This will be described with reference to FIG. First, consider the case where the thickness of the delay plate is the thinnest. Let A be a point on a plane perpendicular to the rotation axis on which the light ray is incident. This ray passes through the spiral slope retarder for a certain distance and reaches point B on the spiral slope.

At this time, if the radius of the disk on which the spiral slope is installed is R, the pitch of the slope is d, and the slope angle of the spiral slope is β, the angle of the light beam incident on the slope is also β. is there. β = tan ^-1 {(d / 2πR)} (4)

The angle of the light beam emitted from the point B into the atmosphere is defined as γ based on the incident direction AB. Assuming that the refractive index of the transmitting material is n, the emission angle γ of the light beam is represented by γ = sin ⁻¹ (n sin β) −β (5) from Snell's law. This light ray is reflected by the vertical reflecting plane mirror 2c and returns to the point A along the reverse path.

Here, consider the case where the delay plate has passed the thickest part. The light beam exits from the point C on the slope and the exit direction is deflected by the angle γ in the same manner as when exiting from the point B. Also in this case, the light is reflected by the vertical plane mirror 2c and follows the reverse path. At this time, the optical path difference between the two paths is 2Bc−
It turns out that it becomes 2BE. Here, BE is traveling in the atmosphere, and BC is traveling in the permeable material.

Accordingly, the difference between the optical path lengths of the light beams passing through the thickest portion and the thinnest portion of the spiral slope delay plate is expressed by the following equation. ΔL _MAX = 2nd−2cos γ (6)

Here, ΔL _MAX is the maximum optical path length difference, n is the refractive index of the transparent material, d is the pitch of the spiral, and corresponds to the distance between BC. At this time, as an example of specific values of the parameters, R = 25 mm, γ = 54 mrad, and the incident light wave number 645
2 cm ^-1 , refractive index n of transmissive material (sapphire glass)
Assuming that 1.746 and d = 8.5 mm, the emission angle becomes 40.4 mrad with respect to the rotation axis, and the maximum optical path length difference is 1.27 cm.
Becomes When this structure is used for a Fourier transform spectroscopic interferometer, the wave number resolution is 0.79 cm ^-1 .

(Embodiment 6) FIG. 8 is a block diagram showing an embodiment of an optical path length scanning mechanism using a spiral staircase delay plate according to an embodiment of the present invention. In FIG. 8, 16 is a spiral staircase reflector, 2d is a vertical reflecting plane mirror, 3 is a rotating disk, 4 is a rotating axis, 5 is a light source, 6 is a collimator lens, 7 is a light splitting mirror,
8 is a fixed reflecting mirror, 9 is a condenser lens, and 10 is a photodetector.

In order to operate this, one of the light split by the light splitting mirror 7 is made incident on the fixed reflecting mirror 8 and the other light is made incident on the spiral step delay plate. The light incident on the step surface and transmitted through the delay plate is reflected by the vertical reflecting plane mirror, passes through the spiral step delay plate again, enters the light splitting mirror 7 again, and is returned to the light returning from the fixed reflecting mirror 8 again. The light is multiplexed and condensed on the photodetector 10 by the condensing lens 9 to obtain an interference signal.

Here, the rotating disk unit 3 is driven to rotate the spiral staircase delay plate 16 around the rotating shaft 4. At this time, the length of the optical path passing through the spiral staircase delay plate 16 can be changed periodically. When the signal of the photodetector 10 is measured in synchronization with the rotation of the rotating disk, an interferogram is obtained, and a spectrum is obtained by performing the Fourier transform.

The principle will be described below. The spiral staircase is a part of a sector in which the circumference of the radius R is equally divided into N, and the step is Δd. The refractive index of the light transmissive material forming the spiral staircase delay plate is represented by n. When making a round around the spiral staircase delay plate, the difference between the optical path length when light passes through the thickest portion of the spiral staircase delay plate and the optical path length when light passes through the thinnest portion is nNΔ.
Since this is d, this is the maximum optical path length difference.

Here, when the parameters are specifically shown, R =
25 mm, N = 2048, Δd = 0.633 μm, incident light wave number 6452 cm ⁻¹ , sapphire glass (n = 1.746) as a transparent material, and optical path length difference ΔL _MAX = 0.4.
5 cm, the wave number resolution is 2.2 cm ^-1 .

The foregoing description of the present invention has been presented only by way of illustration and specific example for purposes of explanation and illustration. Accordingly, it will be apparent to one skilled in the art that the present invention may have many changes and modifications without departing from its essentials.

For example, the light source can be replaced by a fiber light source. The light splitting mirror may be a semi-transparent mirror.
Further, the vertical plane reflecting mirror can be replaced by a corner cube mirror or a corner cube prism.
In this embodiment, the Michelson interferometer is used, but this can be easily replaced with an interferometer such as a Twyman Green interferometer or a Mach-Zehnder interferometer. Further, in this embodiment, the portion through which the light beam passes through the free space can be replaced with a structure via an optical fiber or an optical waveguide, if necessary.

In this embodiment, the cycle of the spiral is one rotation, but this can be changed to an arbitrary cycle such as a half cycle or a 1/3 cycle. Further, the inclination angle of the spiral slope can be arbitrarily changed. Furthermore, the angle of incidence on the spiral slope reflector or the spiral staircase reflector need not be parallel to the rotation axis. Lastly, specific numerical values such as the size of the disk portion and the spiral inclined mirror in the present embodiment are merely examples, and can be changed within a possible range.

In this embodiment, an example in which the present invention is applied to Fourier transform interference spectroscopy is shown. However, it is apparent that the present invention can be used for an optical path length scanning mechanism of an apparatus using an interferometer such as an autocorrelator. .

[0048]

According to the present invention, as a variable optical path delay device, a spiral slope reflecting mirror or a spiral staircase reflecting mirror or a spiral slope delaying plate or a spiral staircase reflecting mirror is used. Long scanning can be performed and downsizing can be achieved. By using this variable optical path delay device, a small, stable, and high-resolution Fourier transform spectrometer can be realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of an interferometer using a variable optical path delay device according to the present invention.

FIG. 2 is an explanatory diagram relating to a variable optical path delay device according to the present invention.

FIG. 3 is a configuration diagram showing an embodiment of an interferometer using the variable optical path delay device according to the present invention.

FIG. 4 is a configuration diagram showing an embodiment of an interferometer using the variable optical path delay device according to the present invention.

FIG. 5 is a configuration diagram showing an embodiment of an interferometer using the variable optical path delay device according to the present invention.

FIG. 6 is a configuration diagram showing an embodiment of an interferometer using the variable optical path delay device according to the present invention.

FIG. 7 is an explanatory diagram relating to a variable optical path delay device according to the present invention.

FIG. 8 is a configuration diagram showing an embodiment of an interferometer using the variable optical path delay device according to the present invention.

FIG. 9 is an explanatory diagram of an interferometer using a conventional optical path length scanning mechanism.

[Explanation of symbols]

 Reference Signs List 1 spiral inclined reflector 1a spiral inclined reflector surface at rotation angle o 1b spiral inclined reflector surface at rotation angle θ 1c spiral inclined reflector surface at rotation angle θ = 2π 2 vertical reflecting flat mirror 2a, 2b vertical reflecting flat mirror 2c vertical reflection Plane mirror 3 Rotating disk part 4 Rotating axis 5 Light source 6 Collimator lens 7 Light splitting mirror 8 Fixed reflecting mirror 9 Condensing lens 10 Photodetector 11a, 11b Deflection mirror 12 Double-sided polished spiral inclined reflecting mirror 13 Spiral stair reflecting mirror 14 Double-sided spiral staircase Reflector 15 Spiral slope delay plate 15a Spiral slope delay plate surface at rotation angle o 15b Spiral slope delay plate surface at rotation angle θ = 2π 16 Spiral delay plate AX Rotation center BS Beam splitter CM Corner cube mirror CL Collimator lens M1a, M1b Deflection mirror LPa, LPb Optical path S Light source

Claims (8)

[Claims] 1. An optical delay device for controlling an optical path length by changing a position of a reflecting mirror, comprising a disk portion rotatable with respect to a central axis, and a mirror formed in a spiral slope around the disk. Then, light is incident on the spiral inclined mirror, and the incident position on the mirror surface is moved in parallel with respect to the incident optical axis by rotation, thereby changing the distance until the incident light reaches the mirror surface. A variable optical path delay device that controls an optical path length through which light incident by rotation passes. 2. The variable optical path delay device according to claim 1, wherein the inclined structure reflects the incident light by using one surface. 3. The variable optical path delay device according to claim 1, wherein the slope structure reflects the incident light using both surfaces. 4. An optical delay device for controlling an optical path length by changing a position of a reflecting mirror, comprising a disk part rotatable with respect to a central axis, and a mirror formed in a spiral step shape around a disk. Then, light is incident on the spiral staircase mirror, and the incident position on the mirror surface is moved in parallel to the incident optical axis by rotation, thereby changing the distance until the incident light reaches the mirror surface. A variable optical path delay device that controls an optical path length through which light incident by rotation passes. 5. The variable optical path delay device according to claim 4, wherein the staircase structure reflects the incident light by using one surface. 6. The variable optical path delay device according to claim 4, wherein the staircase structure reflects light incident using both surfaces. 7. An optical delay device for controlling an optical path length by changing a thickness of a delay plate through which light is transmitted, comprising: a disk portion rotatable with respect to a center axis; Light is incident on the spiral-slope delay plate, and the outgoing position on the spiral-slope is moved parallel to the incident optical axis by rotation, so that the incident light passes through the delay plate. A variable optical path delay device, wherein the distance is changed to control the optical path length through which the light incident by the rotation of the disk passes. 8. An optical delay device for controlling an optical path length by changing the thickness of a delay plate through which light passes, wherein the disk portion is rotatable with respect to a central axis, and the disk portion has a spiral staircase shape. The light is incident on the spiral staircase delay plate, and the incident position on the spiral staircase is moved in parallel to the incident optical axis by rotation, so that the incident light passes through the delay plate. A variable optical path delay device, wherein the optical path length through which light incident through rotation of the disk passes is controlled.